Operational amplifiers are being widely applied. In the operation process of the operational amplifier, due to the working principle and environment effects, a voltage drift occurs so as to output an offset voltage, which affects the measurement sensitivity of the entire system.
Recently, the structural diagram of an existing auto-zero circuit of an operational amplifier is illustrated in FIG. 1, wherein Vi is input voltage, Vo is output voltage, and there are two power-line terminals +VCC and −VEE. Through setting an adjustable resistance to regulate a current between two auto-zero terminals, the offset voltage which the operational amplifier outputs is reduced. However, an artificial auto-zero operational process is more complex and needs a long regulating time, so that is hard to ensure accuracy; simultaneously, the operational amplifier circuit is often built in a fixture, so the artificial auto-zero operation has some limitations.
As a result, it is necessary to provide an auto-zero circuit of an operational amplifier to solve the problems existing in the conventional technologies.